The invention relates to an arrangement for internal passive turbine blade tip clearance control in a high-pressure turbine in which casing segments located above the blade tips of the rotor are supported at their front and rear ends by radially movable guide vane segments and concentric inner rings acting upon them whose thermal expansion and contraction matches the load-dependent expansion or contraction of the rotor to provide controlled radial movement of the casing segments to control the blade tip clearance.
In aircraft gas turbines, the clearance between the blade tips of the rotor of the high-pressure turbine and the non-rotating parts of the casing or liners located at a spacing opposite the blade tips must remain constant under various flight conditions and loads to keep output and fuel losses low in all phases of the flight and to ensure high turbine efficiency. The clearance must also be wide enough to prevent friction of the rotating blade tips on the static parts due to rotor expansion or contraction under transitional conditions such as take-off, landing, acceleration, or deceleration. The width of the clearance must therefore be controlled due to the varying thermal and dynamic load of the rotor in various operating states and the exclusively thermal expansion of the static elements located opposite the blade tips.
A passive automatic clearance control mechanism has been proposed in addition to expensive active clearance width control by a controlled supply of cold or hot air to keep the blade tip clearance at as constant and low a value as possible in all operating phases and to utilize the energy generated effectively without allowing contact of the rotor blade tips with the adjacent static casing parts in a phase of lower thermal and dynamic rotor load.
For example, GB 20 61 396 describes an internal passive control mechanism of the blade tip clearance in which a segmented liner is spaced from the rotor blade tips and supported upstream of the rotor on the outer platforms of the nozzle guide vanes and downstream of the rotor on the outer platforms of guide vanes of a subsequent low-pressure turbine stage. The inner platforms of the guide vane segments on both sides of the high-pressure turbine are each connected with an annular member whose thermal expansions and contractions match those of the high-pressure turbine rotor. The annular members mounted to the guide vane segments on both sides increase or decrease in this internal passive blade tip control system depending on the rotor load and the varying radial expansion or contraction of the rotor disk and blades so that the guide vane segments and the liner segments they support are adjusted in radial direction either outwardly or inwardly. This ensures passive automatic blade tip clearance control as a function of the load conditions in the high-pressure turbine.
However, this internal passive blade tip clearance control system cannot be applied to turbines in which a firm structure downstream of the rotor is missing and where there is no support of the inner ring that is attached to the radially movable guide vane segments. This applies, for example, to turbines in which the downstream rotor does not have a static bearing but sits in a rotating component of the high-pressure turbine, as there is no static rear structure to which annular member that acts on the guide vanes could be attached.